Influence of Residual Stress/Strain on the Biomechanical
Stability of Vulnerable Coronary Plaques: Potential Impact for Evaluating the
Risk of Plaque Rupture- Am J Physiol
Heart Circ Physiol., 293(3):H1987-96, 2007 - In a vulnerable plaque
(VP), rupture often occurs at a site of high stress within the cap. It is also
known that vessels do not become free of stress when all external loads are
removed. Previous studies have shown that such residual stress/strain (RS/S)
tends to make the stress distribution more uniform throughout the media of a
normal artery. However, the influence of RS/S on the wall stress distribution
in pathological coronaries remains unclear. The aim of this study was to
investigate the effects of RS/S on the biomechanical stability of VPs. RS/S
patterns were studied ex vivo in six human vulnerable coronary plaque samples.
Since the existence of RS/S can only be assessed by releasing it, the opening
angle technique was the experimental approach used to study the geometrical
opening configurations of the diseased arteries, producing an arterial wall in
a near-zero stress state. Reciprocally, these opening geometries were used in
finite element simulations to reconstruct the RS/S distributions in closed
arteries. It was found that the RS/S: i) is not negligible, ii) dramatically
affects the physiological peak stress amplitude in the thin fibrous cap, iii)
spotlights some new high stress areas, and iv) could be a landmark of the
lipid core’s developmental process within a VP. This study demonstrates that
plaque rupture is not to be viewed as a consequence of intravascular pressure
alone, but rather of a subtle combination of external loading and intraplaque
RS/S.

Fig. 2: Description of the protocol performed on human specimen I to
obtain the geometry of the macroscopic zero-stress configuration. A)
isolated left anterior descending coronary sample of 4mm length. B)
zero-stress configuration obtained 3 hours after radial sectioning of the
healthy arc. The opening angle was measured as 143°. C) macroscopic
histological observation of the same sample enabling the contours of the
plaque constituents to be defined. D) microscopic histological view of
the thin fibrous cap, from which the cap thickness CTh was approximated (CTh
close to 94 µm). LC= lipid core; CF: cellular fibrosis.